Block copolymer

ABSTRACT

Provided is a lactic acid-based block copolymer which is biodegradable while having excellent mechanical properties.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is based on, and claims priority from, Korean Patent Application No. 10-2018-0001716, filed on Jan. 5, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a block copolymer which is biodegradable, while having excellent mechanical properties.

BACKGROUND OF THE INVENTION

A polylactic acid (PLA) resin is a plant-derived resin obtained from plants such as corn, etc., and has a biodegradable property. It suppresses depletion of petroleum-based resources and emits less carbon dioxide gas, unlike existing petroleum-based resins, such as a polystyrene resin, a polyvinyl chloride (PVC) resin, a polyethylene resin, etc., and thus reduces environmental pollution which is a disadvantage of petroleum-based plastic products. As environmental pollution caused by waste plastics and the like has caused social problems, efforts have been made to expand the application of polylactic acid to various fields, including food packing materials and containers, cases for electronic products, etc., to which general plastics (petroleum-based resins) have been applied.

However, the polylactic acid resin has poor impact resistance and heat resistance as compared with existing petroleum-based resins, and thus is used in limited applications. Further, the polylactic acid resin exhibits brittleness due to poor elongation at break, which is a limitation in a general-use resin.

Accordingly, in the existing technology, studies for improvement of the physical properties have been conducted by compounding polylactic acid with a material having biodegradability and relatively excellent elongation at break, such as PBS (poly(butylene succinate)) and PBAT (poly(butylene adipate-co-terephthalate)), or by forming a block copolymer therefrom. However, since PBS and PBAT have low tensile strength, there is a problem in that the compound or the block copolymer also has low tensile strength.

SUMMARY OF THE INVENTION Technical Problem

The present invention provides a lactic acid-based block copolymer having excellent mechanical properties such as tensile strength and elongation at break while maintaining environmental friendliness and biodegradability.

Technical Solution

According to one embodiment of the present invention, a block copolymer represented by the following Chemical Formula 1 is provided.

In Chemical Formula 1,

X₁ and X₂ are each independently an ester bond, an amide bond, a urethane bond, a urea bond, or a carbonate bond,

L is a substituted or unsubstituted C₁₋₁₀ alkylene; a substituted or unsubstituted C₆₋₆₀ arylene; or a substituted or unsubstituted C₂₋₆₀ heteroarylene containing one or more heteroatoms selected from the group consisting of O, N, Si, and S, and n and m are each independently an integer of 1 to 10,000.

Hereinafter, a block copolymer according to a specific embodiment of the present invention will be described in more detail.

In the present invention, the terms “the first”, “the second”, and the like are used to describe a variety of components, and these terms are merely employed to differentiate a certain component from other components.

The block copolymer according to an embodiment of the present invention can include a first block including a lactic acid-polymerized repeating unit and a second block including a 3-hydroxypropionic acid (hereinafter referred to as 3HP)-polymerized repeating unit, wherein the first block and the second block are linked to each other via an ester bond, an amide bond, a urethane bond, a urea bond, or a carbonate bond, and thus 3HP can compensate for the disadvantage of low elongation at break of a biodegradable resin containing only polylactic acid.

Specifically, the block copolymer according to an embodiment of the present invention can include a first block which is a lactic acid-polymerized repeating unit represented by the following Chemical Formula 3 and a second block which is a 3-HP-polymerized repeating unit represented by the following Chemical Formula 4.

The repeating unit of Chemical Formula 3 is a repeating unit of polylactic acid (PLA), wherein any polylactic acid can be used without limitation, and commercial polylactic acid can be used. The polylactic acid can be commonly prepared from an L-lactic acid-derived monomer and/or a D-lactic acid-derived monomer, and can also include a certain amount of other monomers which are not derived from L-lactic acid or D-lactic acid. There are a variety of methods of preparing the polylactic acid. The most representative known method is ring-opening polymerization of lactide prepared from lactic acid. However, the method is not limited thereto, and the polylactic acid can also be prepared by direct polycondensation of lactic acid. The polylactic acids prepared from L-lactic acid- or D-lactic acid-derived monomers are crystalline and have a high melting point. However, when the polylactic acid is prepared using L-lactide, D-lactide, or meso-lactide derived from L-lactic acid or D-lactic acid, its crystallinity and melting point can be freely controlled according to the content of L-lactide, D-lactide, or meso-lactide, and it is possible to control the content of each component according to the application.

Meanwhile, the repeating unit of Chemical Formula 4 is a repeating unit of poly(3-hydroxypropionic acid) (hereinafter referred to as P(3HP)), which has an advantage of high elongation at break due to excellent mechanical properties and a low glass transition temperature (Tg) of −20° C. Therefore, when the block copolymer is prepared by chemical bonding of P(3HP) and polylactic acid (PLA), it is possible to prepare a material having excellent mechanical properties and biodegradability.

The repeating units of Chemical Formulae 3 and 4 can be linked to each other via an ester bond, an amide bond, a urethane bond, a urea bond, or a carbonate bond, and specifically, X₁ and X₂ in Chemical Formula 1 can each independently be an ester bond, an amide bond, a urethane bond, a urea bond, or a carbonate bond.

Further, L in Chemical Formula 1 can be a substituted or unsubstituted C₁₋₁₀ alkylene; a substituted or unsubstituted C₆₋₆₀ arylene; or a substituted or unsubstituted C₂₋₆₀ heteroarylene containing one or more heteroatoms selected from the group consisting of O, N, Si, and S, and preferably a linear C₈ alkylene.

In Chemical Formula 1, a ratio of n and m can be 1:1 to 10, 1:1.5 to 9, or 1:2 to 8. When a molar ratio of the first block and the second block is less than 1:1, elongation at break of the block copolymer can be reduced, and the block copolymer can be easily broken. When the molar ratio is more than 1:10, impact resistance of the block copolymer can be reduced.

Meanwhile, the block copolymer can be a block copolymer represented by the following Chemical Formula 2.

In Chemical Formula 2, L, n, and m are the same as defined above.

A weight average molecular weight of the block copolymer including the first block and the second block can be 1000 g/mol or more, 2000 g/mol to 500,000 g/mol, 5000 g/mol to 450,000 g/mol, or 10,000 g/mol to 350,000 g/mol. When the weight average molecular weight of the block copolymer is less than 1000 g/mol, elongation at break of the block copolymer can be reduced, and the block copolymer can be easily broken.

The glass transition temperature (Tg) of the block copolymer can differ according to a molar ratio of P(3HP) and PLA. When the molar ratio of P(3HP) and PLA is 1:1 to 10, the glass transition temperature can be 25° C. to 40° C., but is not limited thereto.

The block copolymer of an embodiment can have unique crystallization characteristics in DSC (Differential Scanning calorimeter) patterns. For example, the block copolymer can exhibit two peaks in DSC patterns, specifically, a first peak at a melting point (Tm) of 60° C. to 80° C., or 65° C. to 75° C., and a second peak at a melting point (Tm) of 125° C. to 150° C., or 135° C. to 148° C. From the two peaks in the above-described temperature ranges in DSC patterns, the unique crystallization characteristics of the block copolymer of an embodiment can be confirmed. The block copolymer of an embodiment having the unique crystallization characteristics can exhibit excellent heat resistance, elongation at break, impact resistance, tensile strength, etc.

The block copolymer having the unique crystallization characteristics can have tensile strength of 40 MPa to 55 MPa, 45 MPa to 55 MPa, or 50 Pa to 55 Pa. The block copolymer can have a tensile modulus of 1 GPa to 3.3 GPa, 1.5 GPa to 3.3 GPa, or 2 GPa to 3.3 GPa. The block copolymer can have tensile elongation of 1.8% to 540%, 10% to 540%, or 50% to 540%.

Meanwhile, PLA, P(3HP), and an organic solvent are introduced into a reactor and stirred at 150° C. to 200° C., and a crosslinkable monomer is additionally introduced and allowed to react. A reaction product is dissolved in chloroform, and extracted with methanol to recover the block copolymer.

A molar ratio of PLA and P(3HP) introduced into the reactor can be 1:0.1 to 1, 1:0.3 to 0.9, or 1:0.4 to 0.7. When the molar ratio of the first block and the second block is less than 1:0.1, elongation at break of the block copolymer can be reduced, and the block copolymer can be easily broken. When the molar ratio is more than 1:1, heat resistance and impact resistance of the block copolymer can be reduced.

The crosslinkable monomer can link the respective blocks of PLA and P(3HP) to link the first block and the second block via an amide bond, and for example, the crosslinkable monomer can be a monomer containing a crosslinkable functional group such as an isocyanate group, an amide group, a hydroxyl group, a carboxyl group, an epoxy group, a glycidyl group, an amino group, an alkoxysilyl group, etc.

The crosslinkable monomer containing the isocyanate group can be, for example, 2-isocyanatoethyl (meth)acrylate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, methacryloyl isocyanate, or allyl isocyanate; an acryloyl monoisocyanate compound obtained by reacting a diisocyanate compound or a polyisocyanate compound with 2-hydroxyethyl (meth)acrylate; an acryloyl monoisocyanate compound obtained by reacting a diisocyanate or a polyisocyanate compound, a polyol compound, and 2-hydroxyethyl (meth)acrylate, etc., but is not limited thereto.

The monomer containing the amide group can be, for example, (meth)acrylamide, N-vinyl pyrrolidone, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, diacetone (meth)acrylamide, etc., but is not limited thereto.

The crosslinkable monomer containing the hydroxyl group can be, for example, a monomer containing a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxyethylene glycol (meth)acrylate, glycerol (meth)acrylate, hydroxypropylene (meth)acrylate, etc., and a mixture of one or more of the monomers can also be used, but is not limited thereto.

The monomer containing the carboxyl group can be, for example, (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc., but is not limited thereto.

Further, the crosslinkable monomer containing the glycidyl group can be, for example, an epoxyalkyl (meth)acrylate such as glycidyl (meth)acrylate, epoxycyclohexylmethyl (meth)acrylate, etc., but is not limited thereto.

The monomer containing the alkoxysilyl group can be, for example, 3-(trimethoxysilyl)propyl (meth)acrylate, 2-allyloxyethyl (meth)acrylate, etc., but is not limited thereto.

Advantageous Effects

According to the present invention, a lactic acid-based block copolymer having excellent mechanical properties such as tensile strength and elongation at break while maintaining environmental friendliness and biodegradability is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1, (a) and (b) are graphs showing NMR results of analyzing HDI and a block copolymer of Example 1, respectively; and

FIG. 2 is a graph showing DSC results of analyzing PLA, P3HP, and the block copolymer of Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described in more detail in the following examples. However, the following examples are for illustrative purposes only, and the present invention is not intended to be limited by the following examples.

Example 1

To a 500 mL round-bottom flask, 11 g (number of moles: 0.055 mmol, MW: 200,000 g/mol) of polylactic acid, 2.75 g (number of moles: 0.028 mmol, MW: 100,000 g/mol) of poly(3-hydroxypropionic acid), and 50 ml of toluene were introduced, and stirred at 180° C. for 1 hour. Thereafter, 1,6-hexamethylene diisocyanate (HDI, number of moles: 0.110 mmol, MW: 168.2 g/mol) was added thereto, and allowed to react at 180° C. for 30 minutes. Thereafter, the reaction product was dissolved in chloroform, and then extracted with methanol to recover a block copolymer of the following Chemical Formula 5.

Comparative Example 1

To a 500 mL round-bottom flask, 11 g (number of moles: 0.055 mmol, MW: 200,000 g/mol) of polylactic acid and 50 ml of toluene were introduced, and stirred at 180° C. for 1 hour. To the round-bottom flask, 1,6-hexamethylene diisocyanate (HDI, number of moles: 0.110 mmol, MW: 168.2 g/mol) was added thereto, and allowed to react at 175° C. for 40 minutes under a nitrogen atmosphere. Thereafter, the reaction product was dissolved in chloroform, and then extracted with methanol to recover a copolymer of the following Chemical Formula 6.

Evaluation

1) NMR (Nuclear Magnetic Resonance) Analysis

NMR analysis was performed at room temperature using an NMR spectrometer containing Varian Unity Inova (500 MHz) equipped with a 5 mm triple-resonance probe. HDI and the block copolymer of Example 1 were used as analytes after being diluted with a solvent (CDCl₃) for NMR measurement at a concentration of about 10 mg/ml, respectively, and chemical shifts were expressed as ppm.

FIGS. 1 (a) and (b) are graphs showing NMR results of analyzing HDI and the block copolymer of Example 1, respectively. According to FIG. 1, the NMR peaks of HDI were shifted to the left.

Further, according to the NMR result of the block copolymer of Example 1, a peak corresponding to the N—H bond was observed at about 3.1 ppm, indicating that the PLA block and the P3HP block were linked via a urethane bond.

2) DSC (Differential Scanning Calorimeter) Analysis

DSC analysis was performed using a PerkinElmer DSC 800 instrument. PLA, P3HP, and the block copolymer of Example 1 as analytes were heated using the instrument at a heating rate of 10° C. per minute from 25° C. to 250° C. under a nitrogen atmosphere, respectively, and then cooled at a cooling rate of −10° C. per minute from 250° C. to −50° C., and heated again at a heating rate of 10° C. per minute from −50° C. to 250° C. to obtain endothermic curves.

FIG. 2 is a graph showing DSC results of analyzing PLA, P3HP, and the block copolymer of Example 1. Further, the resulting graph of FIG. 2 was analyzed to determine a glass transition temperature (Tg), a melting temperature (Tm), and an enthalpy of melting (ΔH_(melt)) of each compound, which are shown in Table 1 below.

TABLE 1 Tg (° C.) Tm (° C.) ΔH_(melt) (J/g) PLA 61.85 145.37 2.669 P3HP −25.92 66.99 54.68 Example 1 34.22 62.03 9.296 139.62 12.21

According to Table 1, it was confirmed mat the copolymer of Example 1 showed the melting temperatures of both PLA and P3HP. Random copolymers show no crystallinity, and thus no melting temperatures are observed, whereas block copolymers show melting temperatures of respective blocks. Accordingly, the DSC analysis results confirmed that the compound of Example 1 was a block copolymer.

Further, Example 1 showed a glass transition temperature of 34.22° C. which is between the glass transition temperatures of PLA and P3HP. 

1. A block copolymer of the following Chemical Formula 1:

wherein in Chemical Formula 1: X₁ and X₂ are each independently an ester bond, an amide bond, a urethane bond, a urea bond, or a carbonate bond; L is a substituted or unsubstituted C₁₋₁₀ alkylene, a substituted or unsubstituted C₆₋₆₀ arylene, or a substituted or unsubstituted C₂₋₆₀ heteroarylene including one or more heteroatoms selected from the group consisting of O, N, Si, and S; and n and m are each independently an integer from 1 to 10,000.
 2. The block copolymer of claim 1, wherein the block copolymer is of the following Chemical Formula 2:

wherein in Chemical Formula 2: L is a substituted or unsubstituted C₁₋₁₀ alkylene, a substituted or unsubstituted C₆₋₆₀ arylene, or a substituted or unsubstituted C₂₋₆₀ heteroarylene including one or more heteroatoms selected from the group consisting of O, N, Si, and S; and n and m are each independently an integer from 1 to 10,000.
 3. The block copolymer of claim 1, wherein in Chemical Formula 1, L is a linear C₈ alkylene.
 4. The block copolymer of claim 1, wherein in Chemical Formula 1, a ratio of n and m is 1:1 to
 10. 5. The block copolymer of claim 1, wherein the block copolymer has a weight average molecular weight of 1000 g/mol or more.
 6. The block copolymer of claim 1, wherein the block copolymer has a first peak at a melting point (Tm) of 60° C. to 80° C. and a second peak at a melting point (Tm) of 125° C. to 150° C. in DSC (Differential Scanning calorimeter) patterns.
 7. The block copolymer of claim 1, wherein the block copolymer has a tensile strength of 40 MPa to 55 MPa.
 8. The block copolymer of claim 1, wherein the block copolymer has a tensile modulus of 1 GPa to 3.3 GPa.
 9. The block copolymer of claim 1, wherein the block copolymer has an elongation at break of 1.8% to 540%. 